Recently, semiconductor technologies have been advanced, and thus, semiconductor integrated circuits are becoming larger and have higher functions. On the other hand, it is strongly needed to reduce the consumption power at waiting with regard to portable devices and sensor network and so on. Even though multiple internal circuits are integrated in a semiconductor integrated circuit, all of the internal circuits do not always operate. Therefore, by stopping supplying the power source to the non-operating internal circuit, it is possible to reduce the consumption power.
However, there is a problem that a large inrush current may flow at changing a state where the power source is not supplied to the circuit to a state where the power source is supplied. Due to the inrush current, the supply voltage may vary, which can cause bad influence on the other internal circuit, or cause a gate break-down.